Positioning-triggered handover

ABSTRACT

A method for estimating the location of a terminal operating in a communication system having at least two networks having overlapping areas of coverage, each network supporting at least one method for estimating the location of the terminal, and the terminal being in communication with a first one of the networks, the method comprising: assessing which of the networks is likely to form the more accurate estimate of the location of the terminal; and if that is the first one of the networks, estimating the location of the terminal by means of the first one of the networks, and if that is a second one of the networks, handing over the terminal to the second one of the networks and estimating the location of the terminal by means of the second one of the networks.

This invention relates to handover in communication systems, andespecially to handovers that can assist in enabling the positioning ofdevices operating in such systems.

Positioning or locating services (LCS) are becoming an important aspectof communication systems such as mobile telephony systems. Theseservices allow the location of a user terminal or user equipment (UE) tobe estimated. Knowledge of the location may be of interest to the userof the UE, and can also be used to offer the user additional servicesbased on his location. One valuable advantage is that if the user useshis UE to make a call to the emergency services, knowledge of thelocation of the user could help the emergency services to offerassistance rapidly.

There are a number of ways in which the location of the UE can beestimated, but in one typical way timing differences are calculated forcommunications between the UE and a number of base stations. Using thetiming differences the distance between the UE and each of the basestations can be estimated, and then with knowledge of the locations ofthe base stations the position of the UE can be triangulated.

One example of the types of system in which such services can beprovided is a mobile telephony system, for example a cellular telephonysystem.

On the implementation of the proposed 3G (Third Generation) or UMTS(Universal Mobile Telephony System) system, it is planned that LCS willbe supported by a number of cellular network systems. Examples includeolder GSM (Global System for Mobile Communications) standard networksoperating according to the 3GPP standard for LCS, together with full3G/UMTS standard networks, also standardised by 3GPP.

When a user is communicating in a region where older GSM networks andUMTS networks fully or partially overlap, it is intended that thenetworks and the user's terminal will be capable of operating so thatthe terminal can switch from communicating in one network tocommunicating in another. For example, in the situation where thenetworks' coverage partially overlaps, a user may move from a locationwhere there is coverage from one of the networks to an adjacent locationwhere there is coverage from another of the networks. It is intendedthat as he does so, his terminal will be handed over from the firstnetwork to the second so that the user can continue to communicate. Evenwhen the networks overlap entirely, a user's terminal may be handed overfrom network one to the other, for example to satisfy capacityconstraints.

It can be expected that there will be differences between the LCScapabilities of networks of different standards. For example, themethods that they support for determining the position of a terminal maybe different. As a result, even though their standards are commonly set,there may be differences in the LCS capabilities between the networks.Due to those differences one of the networks maybe better suited thananother to provide LCS for a particular purpose. As a result, when auser's terminal is in a location where there is overlapping coveragefrom two or more interoperable systems and a need to locate the userarises, there can be situations in which a particular one of thenetworks that provides coverage there best fulfils the positioningrequirements in that situation. However, at the time when the needarises to locate the user, the user's terminal might be connected toanother network than the preferred one that is best able to fulfil thepositioning requirements.

There may also be situations where due to the capabilities of the user'sterminal it is more preferable to determine its location using onenetwork than another. For example, the terminal might support the E-OTDmethod in GSM but might not support any of the positioning methodsstandardized for WCDMA (such as IPDL-OTDOA and A-GPS). This situationmay be considered very likely to happen, because location servicesstandards for GSM have been finalized before those of UMTS, and soterminals that support the GSM methods can be expected to be producedfirst.

The current requirements specified by the U.S. FCC Phase II Mandate setout strict requirements for positioning of a users terminal. The FCC'sThird Report and Order (FCC 99-245) in the matter of revision of thecommission's rules to ensure compatibility with Enhanced 911 EmergencyCalling Systems (CC Docket No. 94-102 RM-8143), adopted Sep. 15, 1999,states: “We adopt the following revised standards for Phase II locationaccuracy and reliability: For network-based solutions: 100 meters for67% of calls, 300 meters for 95 percent of calls; For handset-basedsolutions: 50, meters for 67% of calls, 150 meters for 95 percent ofcalls”. Meeting these requirements will require a very high level ofperformance from positioning systems.

There is therefore a need for a means by which the positioning of aterminal can be improved when it is communicating in a network otherthan the one that can best estimate its position.

According to one aspect of the present invention there is provided amethod for estimating the location of a terminal operating in acommunication system having at least two networks having overlappingareas of coverage, each network supporting at least one method forestimating the location of the terminal, and the terminal being incommunication with a first one of the networks, the method comprising:assessing which of the networks is likely to form the more accurateestimate of the location of the terminal; and if that is the first oneof the networks, estimating the location of the terminal by means of thefirst one of the networks, and if that is a second one of the networks,handing over the terminal to the second one of the networks andestimating the location of the terminal by means of the second one ofthe networks.

According to a second aspect of the present invention there is provideda communication system capable of estimating the location of a terminaloperating therein, the communication system comprising at least twonetworks having overlapping areas of coverage, each network supportingat least one method for estimating the location of the terminal theterminal being in communication with a first one of the networks; one ofthe networks being arranged to assessing which of the networks is likelyto form the more accurate estimate of the location of the terminal; andif that is the first one of the networks to cause the location of theterminal to be estimated by means of the first one of the networks, andif that is a second one of the networks, to cause the terminal to behanded over to the second one of the networks and to cause the locationof the terminal to be estimated by means of the second one of thenetworks.

According to a third aspect of the present invention there is provided amethod for estimating the location of a terminal operating in acommunication system having at least two networks having overlappingareas of coverage, each network supporting at least one method forestimating the location of the terminal, and the terminal being incommunication with a first one of the networks, the method comprising:receiving a request for transmission of an estimate of the terminal'sposition to a position handling unit; assessing which of the networks isbest able to provide the position handling unit with the estimate; andif that is the first one of the networks, estimating the location of theterminal by means of the first one of the networks, and if that is asecond one of the networks, handing over the terminal to the second oneof the networks and estimating the location of the terminal by means ofthe second one of the networks. Then the network that has performed thepositioning can transmit the estimate to the position handling unit. Theposition handling unit may be an interface between one or both of thenetworks and an emergency call handling centre.

Preferably at least one method for estimating the location of theterminal that is supported by the first network is different from the oreach such method supported by the second network. Alternatively, thenetworks may have one or more methods (possibly all their methods) incommon; in that case the present invention is still advantageous sincedifferent levels of accuracy may be achieved in different networks due,for example, to their densities of base stations. Examples of suitablemethods include E-OTD, IPDL-OTDOA and A-GPS and other methods describedbelow. The methods used by each network preferably include at least onemethod that makes use of a radio network subsystem of the respectivenetwork to estimate the location of the terminal. In such methods theterminal is preferably located by measuring timing differences for radiotransmissions between the terminal and stations of the radio subsystem.The said estimating of the location of the terminal is preferablyperformed by such means.

Preferably the first network is operable according to a first standardand the second network is operable according to a second standarddifferent from the first standard. Alternatively the networks may be ofthe same type.

Most suitably the first network is operable according to a standard thatprovides for backward compatibility or another form of interoperabilitywith the second standard.

One or both of the standards may be UMTS or a derivative thereof. One orboth of the standards may be GSM or a derivative thereof. In onesuitable embodiment the first standard is UMTS or a derivative thereofand the second standard may be GSM or a derivative thereof. Both of thestandards could be cellular radio standards, but other arrangements arepossible: for example, one network could be a radio cellular network andthe other a WLAN (wireless local area network) network.

Preferably the terminal is capable of communicating by radio with radioaccess subsystems of the first and second networks and each network isarranged to estimate the location of the terminal by means of itsrespective radio access subsystem.

The said assessing step may be performed by the first network,preferably by an element of a radio access subsystem of the firstnetwork, and most preferably by a controller of that subsystem.

Preferably the method comprises the step of initiating an emergency callby means of the terminal through the first network, and the step ofhanding over the terminal to the second one of the networks compriseshanding over the call to the second one of the networks. In response tothe initiation of such a call a nit of the communication system (forinstance an MSC) may issue a request for an estimate of the location ofthe terminal that initiated the call. That request may be sent to thenetwork through which the call was initiated. The said assessing stepmay be performed in response to that request. Alternatively, other stepsmay be performed in response to that request, and the said assessingstep may be performed in response to one or more outcomes of those othersteps. For instance, in response to the said request may be performedthe step of determining whether the first network is capable ofestimating the location of the terminal to within a pre-set tolerance.The pre-set tolerance may be a specified or requested tolerance. If itis then the location of the terminal is estimated by means of the firstone of the networks. Otherwise preferably said assessing step isperformed.

The handover of the terminal suitably involves transfer of immediatecommunication with and control of the terminal from one network toanother. Where a call is in operation to or from the terminal at thetime that the handover occurs the call is preferably maintained duringand after the handover, but rerouted through the target network.

The terminal may support one or more positioning methods. It may be thatthe terminal does not support any positioning methods that are in commonwith the first network.

The roles of the first and second networks may be reversed. There may bethree or more networks.

After the positioning step has been completed the terminal may be handedover to the first network. This may be initiated by the second network.On or in initiating the handover of the terminal to the first networkthe second network may transmit to the second network a messagerequesting limitation of the conditions under which the terminal may behanding over to the first network. That limitation may be a limitationthat such handover to the first network should not occur until a settime has elapsed, or until the second network has estimated the positionof the terminal.

The present invention will now be described by way of example withreference to the accompanying drawing.

IN THE ACCOMPANYING DRAWING

FIG. 1 is a schematic diagram of a telecommunication system includingtwo networks, and illustrating the operation of a positioning operation.

In the system of FIG. 1, if—when a user's terminal needs to bepositioned—it is determined that the user's terminal is operating in onenetwork but there is another overlapping network that could betterfulfil the positioning operation, then the user's terminal is handedover to the other network and the location of the user's terminal isestimated by that network. Then, if appropriate, after the positioninghas been completed the user's connection can be transferred back to thenetwork with which it was originally connected.

In the following description the positioning of a terminal during anemergency call is described. However, this is just one example of thesituations in which positioning can be used and the present invention isnot restricted to use with emergency calls.

FIG. 1 illustrates a procedure for performing an intersystem handovertriggered by a positioning request which can not be fulfilled by thenetwork initially serving a terminal (the “initial network”), and thesubsequent positioning in another network (the “target network”).

FIG. 1 shows a system including radio access subsystems of two types ofcellular telephony networks: a UMTS RAN (radio access network) 20 and aGSM BSS (base station subsystem) 21. The radio access subsystems areserved by a common MSC (mobile switching centre) 22. The mobileswitching centre is linked to a GMLC (gateway mobile location centre)23, which can determine the location of mobile terminals such as userequipment 24 operating in a linked network. In the present example, theMSC and the GMLC are linked to an emergency call centre 25, termed aPSAP (public safety access point).

The present example relates to the operation of the system in relationto emergency calls. In this example, the following steps take place.

-   1. Terminal 24 is operating in communication with the UMTS network    and its radio access subsystem 20. An emergency call (typically a    call to 112, 999 or 911) is made by the user of terminal 24.-   2. The call passes to MSC 22, which identifies it as being an    emergency call. The MSC therefore routes the call to the PSAP where    it can be answered by an operator. The route of the call is shown by    path 1 in FIG. 1. The MSC also initiates a positioning procedure to    estimate the location of the terminal 24 that has originated the    call. It does this by sending a RANAP LOCATION REPORTING CONTROL    message to the appropriate serving RNC (radio network controller)    26. The Client Type parameter in the message indicates Emergency    Services. This message is shown by path 2 in FIG. 2.-   3. The serving RNC 26 analysis the positioning request message and    determines that it is positioning request relating to an emergency    call. It checks the positioning methods available to it in relation    to the subject terminal 24 to determine the level of accuracy with    which it can estimate that terminal's position, and compares that    expected accuracy with the accuracy required for emergency    positioning (e.g. as specified in FCC 99-245). The MSC can inform    the serving RNC of the required accuracy.

If it is determined that the requirements can be met then the RNC caninitiate positioning of the terminal by means of the subsystem 20 of thenetwork through which the terminal initiated the emergency call. In thissituation it responds to the MSC with its estimate of the terminal'slocation.

However, the accuracy may be limited by the configuration of thatsubsystem or by the level of capability that the terminal 24 has. Forexample, the terminal might not support the positioning methods of thesubsystem 24. If it is determined that the requirements might not be metthen the RNC estimates whether the position of the terminal 24 is likelyto be estimated more accurately by the subsystem 21 of the targetnetwork. If so, it initiates handover of the terminal to the othernetwork. The RNC may initiate handover under other conditions: forinstance, irrespective of any requirements it may initiate handover ifit determines that the position of the terminal 24 is likely to beestimated more accurately by the subsystem 21 of the target network.

If handover is initiated the RNC does not reply to the MSC with anestimate of the user's location. Instead, the RNC initiates handover tothe target network (in this example a GSM network). This is shown bypath 3 in FIG. 1.

The handover request may be a normal handover request. However, it maybe advantageous for the request to include information to indicate thatthe terminal is not to be handed back to the initial networkimmediately. In normal circumstances intersystem handover may betriggered if the communication conditions with a terminal aresignificantly better with one network than with another. Ifcommunication conditions between the terminal and the target networkwere significantly worse than those between the terminal and the initialnetwork then it could happen that immediately after the present handoverthe terminal could be handed back to the initial network. This wouldprevent the target network from performing the positioning itself.Therefore, the intersystem handover request may include information toinhibit such a situation from occurring. The information may be passedin the form of the message or in a parameter attached to the message.The information may specify that the terminal is not to be handed backto the initial network until positioning has been performed, or that itis not to be handed back to the initial network until a set period oftime has elapsed.

-   4. The call initiated by terminal 24 is handed over to the target    network so that terminal is now served by radio access subsystem 21.    As normal, the MSC is aware that intersystem handover has taken    place. After the handover has taken place the MSC reinitiates the    positioning procedure by transmitting another positioning request,    this time to the GSM BSS 21. This is shown by path 4 in FIG. 1.    Messages for individual positioning methods are suitably transferred    as described in 3GPP TS 03.71 (Rel-98, Rel-99) or 3GPP TS 43.059    (Rel-4 onwards). This step could be omitted if the details of the    positioning request were carried in the intersystem handover request    message.-   5. The subsystem 21 estimates the position of the terminal 24 and    returns its position estimate to MSC 22. The subsystem 21 may    include a positioning component for performing this function. For    example, n the case of a GSM system the position estimate is    generated by the SMLC (serving mobile location centre), and in UMTS    relevant functions are provided by functional components of the RNC.    This message is shown by path 6 in FIG. 1.-   6. The MSC 22 forwards the position estimate to GMLC in a MAP    SUBCRIBER LOCATION REPORT message. This is shown by path 7 in    FIG. 1. The GMLC stores the initial position information and other    relevant information about the emergency call in order to support    subsequent location retrieval (NCAS Pull) from the PSAP. The GMLC    also acknowledges the receipt of the location information.-   7. The PSAP requests from the GMLC the initial position of the    emergency caller. This is shown by path 8 in FIG. 1.-   8. The GMLC provides the initial position estimate to the PSAP. This    is shown by path 9 in FIG. 1. With the estimated location of the    terminal 24 an operator at the PSAP can direct emergency support    such as police, fire services or an ambulance to the user's    location.

In this example the decision to initiate intersystem handover is takenby a UMTS RNC. Other network entities, in UMTS and GSM systems, couldmake the decision. To avoid unnecessary intersystem handovers, theunit(s) making such decisions should preferably have knowledge of:

-   a. the extent of overlap of coverage between networks—so that it can    be determined which networks are candidates for fulfilling a    positioning request;-   b. the networks' positioning capabilities (e.g. which positioning    protocols they support)—so that the likely accuracy of positioning a    terminal of certain capabilities can be properly judged; and-   c. the methods of positioning with which the terminal is compatible.

It may also be desirable for those unit(s) to have knowledge of anyrequirements for positioning accuracy.

The assessment of which network is likely to provide the best positionestimate can be triggered by a number of factors. In the above exampleit was triggered by the Client Type parameter received in thepositioning request. Another example is for the assessment to betriggered by a requested quality of service (QoS) in the positioningrequest.

Alternatively, or in addition, account could also be taken of thenetworks capabilities for sending information on the position estimateto the PSAP. If for some reason (e.g. incompatibility or fault) one ofthe networks cannot transmit a position estimate to the PSAP thenhandover may be performed to another network that can do so, in the waydescribed above.

The present approach applicable in the circuit switched (CS) and packetswitched (PS) domains. In the PS domain instead of the above-describedform of intersystem handover, network initiated intersystem cellreselection would be performed.

The approach described above could be used in situations other thanemergency calls. For example, an accurate location of a terminal may bedesired to locate a stolen terminal or to allow a taxi to be routedprecisely to someone who is unsure of their location. In the latter casea surcharge for accurate positioning could be made to the user of theterminal or to the entity (e.g. the taxi company) who requested theaccurate estimate.

The present invention is preferably implemented, in a system operableaccording to the UMTS or GSM standard or a derivative thereof. However,it could be implemented in other systems. It is not limited to cellularradio telephony systems.

Non-limiting examples of positioning methods that may be supported byone or more networks in the present system include the following:

-   -   Global Positioning System (GPS) or other satellite-based or        assisted positioning systems. Enhanced observed time difference        (E-OTD).    -   Time of arrival (TOA).    -   Timing advance (TA).    -   Network-assisted GPS (A-GPS)    -   Observed time difference of arrival—idle period downlink        (OTDOA-IPDL)    -   Cell ID

The standardisation of such methods for GSM is covered in chapters 4.2to 4.4 of the 3GPP standard TS 03.71. The standardisation of suchmethods for UMTS is covered in chapter 4.3 of the 3GPP standard TS25.305.

The applicant hereby discloses in isolation each individual featuredescribed herein and any combination of two or more such features, tothe extent that such features or combinations are capable of beingcarried out based on the present specification as a whole in the lightof the common general knowledge of a person skilled in the art,irrespective of whether such features or combinations of features solveany problems disclosed herein, and without limitation to the scope ofthe claims. The applicant indicates that aspects of the presentinvention may consist of any such individual feature or combination offeatures. In view of the foregoing description it will be evident to aperson skilled in the art that various modifications may be made withinthe scope of the invention.

1. A method comprising: receiving a request for a location of aterminal, the request including an accuracy requirement for the locationof the terminal; in response to receiving the request, assessing whichnetwork of a communication system having at least two networks withoverlapping area of coverage will more accurately determine a locationof the terminal, wherein each network of the at least two networkssupports at least one method of determining the location the terminal,and wherein the terminal is in communication with a first one of thenetworks; determining whether the first one of the network is capable ofdetermining the location of the terminal to within a preset tolerance,and when the first network is capable of determining the location of theterminal to within the preset tolerance the location of the terminal isdetermined using of the first one of the networks; and when the firstone of the networks is the network that will more accurately determinethe location, initiating determining the location of the terminal usingthe first one of the networks, and when a second one of the networks isthe network that will more accurately determine the location, initiatinghanding over the terminal to the second one of the networks fordetermining the location of the terminal using the second one of thenetworks.
 2. The method of claim 1, wherein at least one method ofdetermining the location of the terminal that is supported by the firstnetwork is different from the method supported by the second network oris different from each such method supported by the second network. 3.The method of claim 1, wherein the first network is configured accordingto a first standard and the second network is configured according to asecond standard different from the first standard.
 4. The method ofclaim 3, wherein the first standard is configured to provide forbackward compatibility with the second standard.
 5. The method of claim3, wherein the first standard is universal mobile telecommunicationsystem or a derivative thereof.
 6. The method of claim 3, wherein thesecond standard is global system for mobile communication or aderivative thereof.
 7. The method of claim 1, wherein the terminal isconfigured to communicate by radio with radio access subsystems of thefirst and second networks and each network is configured to determinethe location of the terminal using its respective radio accesssubsystem.
 8. The method of claim 1, wherein the assessing is performedby the first network.
 9. The method of claim 1, further comprising:initiating an emergency call using the terminal through the firstnetwork, wherein handing over the terminal to the second one of thenetworks comprises handing over the call to the second one of thenetworks.
 10. A system comprising: at least two networks havingoverlapping areas of coverage, wherein each network is configured tosupport at least one method of determining location of a terminal; andthe terminal, wherein the terminal is configured to be in communicationwith a first one of the networks, wherein one of the networks isconfigure to, receive a request for a location of the terminal, therequest including an accuracy requirement for the location of theterminal, in response to receiving the request, assess which network ofthe networks will more accurately determine the location of theterminal, determining whether the first one of the network is capable ofdetermining the location of the terminal to within a preset tolerance,and when the first network is capable of determining the location of theterminal to within the preset tolerance the location of the terminal isdetermined using the first one of the networks, when the first one ofthe networks is the network that will more accurately determine thelocation, the system is configured to cause the location of the terminalto be determined using the first one of the networks, and when a secondone of the networks is the network that will more accurately determinethe location, the system is configured to cause initiate the terminal tobe handed over to the second one of the networks and to cause thelocation of the terminal to be determined using the second one of thenetworks.
 11. An apparatus comprising: a processor configured to receivea request for a location of a terminal, the request including anaccuracy requirement for the location of the terminal, the processorbeing in a first one of at least two networks having overlapping areasof coverage, each network supporting at least one method of determiningthe location of the terminal operating therein, wherein the terminal isoperating in the first one of the networks, and in response to receivingthe request, assess which network of the networks is best able toprovide a position handling unit with the location of the terminal, inresponse to receiving the request, assess which network of the networksis best able to provide a position handling unit with the location ofthe terminal, determining whether the first one of the network iscapable of determining the location of the terminal to within a presettolerance, and, when the first one of the network is capable ofdetermining the location within the preset tolerance, to determined thelocation of the terminal, when the first one of the networks is thenetwork that is best able to provide the position handing unit with thelocation, initiating determining the location of the terminal, and whena second one of the networks is the network that is best able to providethe position handing unit with the location, initiating handing over theterminal to the second one of the networks for determining the locationof the terminal using the second one of the networks.
 12. The apparatusof claim 11, wherein the first network is configured according to afirst standard, wherein the second network is configured according to asecond standard different from the first standard, and wherein theapparatus is configured to operate in the first network according to thefirst standard.
 13. The apparatus of claim 12, wherein the firststandard is configured to provide for backward compatibility with thesecond standard.
 14. The apparatus of claim 12, wherein the firststandard is universal mobile telecommunications system or a derivativethereof.
 15. The apparatus of claim 12, wherein the second standard isglobal system for mobile communication or a derivative thereof.
 16. Theapparatus of claim 11, wherein the apparatus is configured to determinethat the request relates to an emergency call and to hand over the callto the second network when the second network is better able to providethe position handling unit with the location.
 17. An apparatuscomprising: receiving means configured to receive a request for alocation of a terminal, the request including an accuracy requirementfor the location of the terminal; assessment means configured to, inresponse to receiving the request, assess which network of at least twonetworks having overlapping areas of coverage is best able to provide aposition handling unit with the location of the terminal; determiningmeans configured to determine whether a first one of the network iscapable of determining the location of the terminal to within a presettolerance and determined the location of the terminal when the first oneof the network is capable of determining the location within the presettolerance; initiation means configured to initiate determining thelocation of the terminal, when the network that is best able to providethe position handling unit with the position is the first one of thenetworks, and the terminal is connected to the first one of thenetworks; and handover means configured to initiate handing over theterminal to a second one of the networks for determining the location ofthe terminal using the second one of the networks, when the network thatis best able to provide the position handling unit with the position isthe second one of the networks.
 18. The apparatus of claim 17, whereinthe first network is configured according to a first standard, whereinthe second network is configured according to a second standarddifferent from the first standard, and wherein the apparatus comprisesoperation means configured to operate the first network according to thefirst standard.
 19. The apparatus of claim 18, wherein the firststandard is configured to provide for backward compatibility with thesecond standard.
 20. The apparatus of claim 18, wherein the firststandard is universal mobile telecommunications system or a derivativethereof.
 21. The apparatus of claim 18, wherein the second standard isglobal system for mobile communication or a derivative thereof.
 22. Theapparatus of claim 17, further comprising: determination meansconfigured to determine that the request relates to an emergency call,and wherein the hand over means is further configured to handover thecall to the second network when the second network is best able toprovide the position handling unit with the location.
 23. A computerprogram, embodied on a computer readable medium, the computer programconfigured to control a processor to perform the method comprising:receiving a request for a location of a terminal, the request includingan accuracy requirement for the location of the terminal; in response toreceiving the request, assessing which network of a communication systemcomprising at least two networks having overlapping areas of coveragewill more accurately determine the location of the terminal, whereineach network of the at least two networks supports at least one methodof determining the location of a terminal wherein the terminal is incommunication with a first one of the networks; determining whether thefirst one of the network is capable of determining the location of theterminal to within a preset tolerance, and, when the first one of thenetwork is capable of determining the location of the terminal to withinthe preset tolerance the location of the terminal is determined using ofthe first one of the networks; and when the first one of the networks isthe network that will more accurately determine the location, initiatingdetermining the location of the terminal using the first one of thenetworks; and when a second one of the networks is the network that willmore accurately determine the location, initiating handing over theterminal to the second one of the networks for determining the locationof the terminal using the second one of the networks.